I've got a dual boot Ubuntu/Windows 8.1 on my machine. Since I updated Windows to 8.1 my Grub menu disappeared.
I already tried to follow at least 5 or 6 guides and answers here on askubuntu, but nothing seems to work.
I ran Ubuntu using Live USB, I used Boot-Repair but something went wrong.
If I click on Reccomended repair I get this error:
GPT detected. Please create a BIOS-Boot partition (>1MB, unformatted filesystem, bios_grub flag). This can be performed via tools such as Gparted. Then try again. Alternatively, you can retry after activating the [Separate /boot/efi partition:] option.
So I tried to set my sda9 (I think that it's the Ubuntu system partition, since it's ext4) with the bios_grub flag and then to run Boot-Repair again. It didn't work.
I don't know what to do. My Grub was working fine (using UEFI) before I updated Windows.
EDIT: I removed the bios_grub flag. Then I used
fsckand it didn't find any error. So I tried again with Boot-Repair but it always gives me the "GPT detected" error. My boot is on UEFI mode, Secure Boot is "off".
When I boot my PC with SecureBoot OFF, I can reach the GRUB menu. But it's empty (the only voice is "System Setup").
EDIT2: Another useless try. I mounted my Ubuntu system disk:
sudo mount /dev/sda9 /mnt
and the other things:
sudo mount --bind /dev /mnt/dev sudo mount --bind /proc /mnt/proc sudo mount --bind /sys /mnt/sys
I logged on the system with
sudo chroot /mnt
I re-installed grub:
grub-install /dev/sda update-grub2
But it still doesn't work.